1. Field
This document relates to a stereoscopic image display device and a driving method thereof capable of implementing a three-dimensional stereoscopic image (hereinafter, referred to as a “3D image”).
2. Related Art
A stereoscopic image display device implements 3D images using a stereoscopic technique and an autostereoscopic technique.
The stereoscopic technique uses binocular parallax images which are great in the stereoscopic effect, which has a type of using glasses and a type of not using glasses, and both the types are put into practical use. In the type of not using glasses (“glassless type”), the stereoscopic images are implemented by dividing optical axes of binocular parallax images, by using optical plates such as parallax barriers provided at front or rear surfaces of a display panel. In the type of using glasses (“glasses type”), binocular parallax images are displayed on a display panel, and polarization glasses or liquid crystal shutter glasses are used to implement stereoscopic images.
The liquid crystal shutter glasses type displays left images and right images on a display element with frame units, and implements 3D images by opening and closing left and right shutters of liquid crystal shutter glasses in synchronization with the display timings. The liquid crystal shutter glasses open only their left shutter during odd frame periods when the left images are displayed, and open only their right shutter during even frame periods when the right images are display, thereby creating binocular parallax in a temporal division manner. In the liquid crystal shutter glasses type, the luminance of the 3D images is low due to the short data turned-on time of the liquid crystal shutter glasses, and 3D crosstalk considerably occurs depending on the synchronization between the display element and the liquid crystal shutter glasses, and on-and-off state switching response characteristics.
The polarization glasses type includes a patterned retarder 2 which is attached to a display panel 1 as shown in FIG. 1. The polarization glasses type alternately displays left image data L and right image data R on the display panel 1 with horizontal line units and switches polarization characteristics incident to the polarization glasses 3 via the patterned retarder 1. Thereby, the polarization glasses type can implement 3D images by spatially dividing left images and right images.
In this polarization glasses type, when source data including image information for left eye and right eye is input, the source data is converted into a line-by-line type data to be suitable for a stereoscopic image display device and is displayed on the display panel 1, thereby creating binocular parallax.
A side-by-side type as in FIG. 2 is most widely used to transmit 3D images. In order to convert a side-by-side type input 3D image into a line-by-line type 3D image, an up-scaling is required to be performed in the horizontal direction (960→1920), and further a down-sampling or a down-scaling is required to be performed in the vertical direction as shown in FIG. 2 (1080→540). Here, “540” indicates resolution taken up by left image data or right image data when the vertical resolution of 3D images is realized by FHD (Full High Definition) (1920(width)×1080(height)). However, in the case where the resolution of input 3D images such as a 3D bluray disc is 1920×2 (width)×1080p (height), the up-scaling in the horizontal direction is not necessary.
Through the down-sampling, odd numbered line information of side-by-side type left image data is input to the odd numbered display lines of the display panel as shown in (1) of FIG. 2, and even numbered line information of side-by-side type right image data is input to the even numbered display lines of the display panel as shown in (1) of FIG. 2.
Through the down-scaling, information obtained by taking an arithmetic average of side-by-side type left image data by two lines as shown in (2) of FIG. 2 is input to the odd numbered display lines of the display panel, and information obtained by taking an arithmetic average of side-by-side type right image data by two lines as shown in (2) of FIG. 2 is input to the even numbered display lines of the display panel.
However, when the above-described down-sampling or the down-scaling is performed for the input 3D data, there is a problem in that display quality is deteriorated for the following reasons.
FIG. 3 shows simulation results that the down-sampling and the down-scaling are respectively performed for an original image #1 having the same left image data and right image data. In the case of the down-sampling, a form difference between the left image and the right image becomes great as shown in (1) of FIG. 3, and thus it is difficult to recognize correct information when polarization glasses are worn. In contrast, in the case of the down-scaling, the left image and the right image have the same form as shown in (2) of FIG. 3, information is easily to be recognized, but there is a disadvantage in that blurring remarkably occurs due to reduction in a spatial frequency resulting from the arithmetic average. Here, the reduction in a spatial frequency means that the sharpness of an image is reduced.
FIG. 4 shows simulation results that the down-sampling and the down-scaling are respectively performed for an original image #2 having the same left image data and right image data. FIG. 4 shows lines having a lower spatial frequency than fonts in FIG. 3. In FIG. 4, the case of the down-scaling ((1) of FIG. 4) achieves an effect better than the case of the down-scaling ((2) of FIG. 4) in terms of removing the difference between the left image and the right image. The difference between the left and right images in FIG. 4 becomes larger in a case where horizontal displacement is great D1 than in a case where it is small D2. This is because, since left images and right images are alternately displayed on the stereoscopic image display device, the horizontal displacement according to one horizontal line displacement is great at diagonal lines with a small slope and boundaries of arc shapes when observation is performed at close range. However, in the case of the down-scaling as well, the spatial frequency is considerably reduced as compared with that of the original image.